The present invention relates to a lens for use with an optical disk or high-density information recording medium.
Lenses employed in reading or writing high-density information on optical disks are required to have resolutions as high as about 1 .mu.m in order to permit detection of densely packed signals. In addition, the light sources used with optical disks experience variations in wavelength, causing changes in the focal point and aberrations which are sometimes too great to be neglected depending on the precision required for the operation of the optical disk.
The environment in which such lenses are used is becoming increasingly hostile, particularly in terms of temperature changes. Therefore, depending on the degree of a certain temperature change and the precision required for the operation of the optical disk, the temperature change may cause significant variations in the focal point and aberrations.
While many lenses have been proposed in the past for use with optical disks, little consideration has been given to variations in wavelength (i.e., chromatic aberration) or to temperature changes.